2) Steps to setup IP over IP tunnel (IPIP tunnel) on Redhat Linux
Layer-3 GRE Tunnels
Example for Establishing an IPSec Tunnel Through Negotiation Initiated by the Branch User That Dynamically Obtains an IP Address - AR500, AR510, and AR530 V200R007 CLI-based Configuration Guide - VPN - Huawei
Forward a public or static IP address from OpenVPN Tunnel — HideConnect VPN Service
Implementing Tunnels - Cisco
About the IP Tunnel Feature - Administering TCP/IP Networks, IPMP, and IP Tunnels in Oracle® Solaris 11.3